Cardiac function management systems are used to treat heart arrhythmias. Pacemaker systems are commonly implanted in patients to treat bradycardia (i.e., abnormally slow heart rate). A pacemaker system includes an implantable pulse generator and leads, which form the electrical connection between the implantable pulse generator and the heart. An implantable cardioverter defibrillator (“ICD”) is used to treat tachycardia (i.e., abnormally rapid heart rate). An ICD also includes a pulse generator and leads that deliver electrical energy to the heart. These systems are also useful in the treatment of heart failure, which is often caused by bundle branch block that can disrupt synchrony between the right and left ventricles. For example, cardiac resynchronization therapy (“CRT”) (also commonly referred to as biventricular pacing) is an emerging treatment for heart failure, which involves stimulation of both the right and the left ventricles to increase hemodynamic efficiency and cardiac output.
The beating heart produces a series of auditory vibrations (i.e., heart sounds) that can be characterized by intensity, frequency, quality, and timing with respect to the cardiac cycle. Two of the normal heart sounds, commonly known as the S1 and S2 sounds, relate to closing of various heart valves. Specifically, the S1 sound is generated by the closing of the mitral and tricuspid valves and thus generally correlates to the onset of ventricular systole, and the S2 sound is generated by the closing of the pulmonary and aortic valves and thus generally correlates to the onset of ventricular diastole. These sounds may also indicate problems or abnormalities in the pumping process, such as for example a murmur or mitral regurgitation. There is thus a need for a cardiac rhythm management device that includes a sensor for sensing heart sounds.